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Previous neuroimaging studies have shown that executive processes requiring planning and set-shifting [e.g. Montreal card sorting task (MCST)] may engage the dorsolateral prefrontal cortex (DLPFC) while inducing dopamine (DA) release in the striatum. However, functional imaging studies can only provide neuronal correlates of cognitive performance and cannot establish a causal relation between observed brain activity and task performance. In order to investigate the contribution of the DLPFC during set-shifting and its effect on the striatal DAergic system, we applied continuous theta burst stimulation (cTBS) to left and right DLPFC. Our aim was to transiently disrupt its function and to measure MCST performance and striatal DA release during [11C]raclopride PET. cTBS of the left DLPFC impaired MCST performance and DA release in the ipsilateral caudate–anterior putamen and contralateral caudate, as compared to cTBS of the vertex (control). These effects were limited only to left DLPFC stimulation but not right DLPFC. This is the fi rst study showing that cTBS, by disrupting left DLPFC function, may indirectly affect striatal DA release during performance of executive tasks. This cTBS-induced regional prefrontal effect and modulation of the frontostriatal network may be important for understanding the contribution of hemisphere laterality and its neural bases with regard to executive functions, as well as for revealing the neurochemical substrate underlying cognitive defi cits.
Due to technological advances in electrophysiology, there is renewed interest in the analysis of local field potentials recorded at many sites simultaneously. In this paper the main problems related to the analysis of LFP are presented, and recent developments in the data analysis methods are reviewed. The focus of the paper is on reconstruction of current source density from extracellular recordings and on decomposition of neural activity into meaningful components.
Learning and memory effects of angiotensin II (Ang II) microinjected unilaterally (left or right) and bilaterally into hippocampal CA1 area on the background of the inhibited hippocampal angiotensin 1 receptors type (ATI) of male Wistar rats were studied. It was found that the combination (losartan 100 ^g + Ang II 0.5^g) microinjected bilaterally or into the left CA1 area improved learning and memory in shuttle-box and step through behavioral tests as compared to the respective controls. The effects were more pronounced after injection into the left CA1 area as compared to the right-side. These findings suggest thatAng II infused on the background of the inhibited CA1 hippocampal AT1 receptors ameliorated the cognitive processes. The data show also an asymmetric effect of Ang II on learning and memory processes in the hippocampus. The stronger modulating effect after microinjection of the combination (losartan + Ang II) into the left CA1 hippocampal area suggests a leftward bias in the rat. The results point to a differential distribution of angiotensin II receptors modulating the learning and memory processes in the left and right hippocampal CA1 area.
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